ML20077N482
| ML20077N482 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/05/1991 |
| From: | Clement C, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| MP-91-641, NUDOCS 9108140333 | |
| Download: ML20077N482 (2) | |
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(20h t t fr f>000 Docket No. 50-423 Re: 10CFR50.36 August 5, 1991 MI'-91-641 U. S. Nuclear Reculatory Commission Document Control Desk Washington, DC 20555 Gentlemen:
hiillstone Nuclear Power Station, Unit No. 3 Malfunctionine Loose Parts Monitor Channel This Special Report is being cubmitted pursuant to hiillstone Unit 3 Technical Specification 3.3.3.8.a: Loose Parts Detection System. Plant Technical Specification 3.3.3.8.a requires that a Special Report be submitted to the NRC 10 days following one or more channels of the Loose Parts Detection System being declared inoperable for more than 30 days, while in hiode 1 (Power Operation) or 2 (Startup).
On June 26,1991, at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, with the plant in hiode 1 (Power Operations) at 100G power,2250 psia and $57 degrees Fahrenheit, LPM Channel 3 was declared inoperable.
The other eleven (11) LPM channels were operating normally.
Loase parts impacts in the Reactor Coolant System (RCS) are detected by accelerometers attached to major RCS components. Channel 3 monitors Loose Parts activity in the Reactor Head. An impact generates an electrical signal from one or more accelerometers, which trippers the LPM to record information from all twelve channels on a computer disk, and actuates an alarm on the main control board.
After declaring LPM Channel 3 inoperable on June 26,1991, a preliminnry investigation determined that the root cause of the Channel 3 failure was degradation of the channel's monitoring signal. The signal was evaluated by an off-site Engineering Department.
The evaluation determined that the signal had degraded to an unacceptable level. The associated pre-ampitfier unit at the containment boundary penetration, ud wiring up to the Control Room, was investigated and determined to be operating satisfactorily. Based on the troubleshooting results, it was, concluded that the LPh1 Channel 3 problem was located inside the Containment, m ociac e, n o.: m pd h[7((((
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' ' ' ' ' [On July 31,1991, while the plant was shutdown for maintenance, a containment entry was made to repair LPhi Channel 3.
The micro-dot cable connector to the l
accelerometer for LPhi Channel 3 was replaced at that time. Operabilit) of LPhi Channel 3 will be verified prior to returning the plant to full power.
The Licensee contact for this Special Report is Burtel N. Forrest, who may be contacted at (203) 444-$442.
Very truly yours.
NOP.THEAST NUCLEAR ENERGY COh1PANY FOR: Stephen E. Scace Director, hiillstone Station BY:
arl H. Cleme t hiillstone Unit 3 Director SES/BNF:cle cc:
T. J. h1artin, Region 1 Administrator W. J. Raymond. Senior Resident ins sector, hiillstone Units Nos.1, 2, and 3 D. H. Jaffe, NRC Project hianager Afillstc.ne Unit Nos. 1 and 3 l
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